docs: def set_metadata(self, metadata, utf8):
          """Sets document metadata.
  
          The ``PDF_METADATA_CREATE_DATE`` and ``PDF_METADATA_MOD_DATE``
          values must be in ISO-8601 format: YYYY-MM-DDThh:mm:ss. An optional
          timezone of the form "[+/-]hh:mm" or "Z" for UTC time can be appended.
          All other metadata values can be any UTF-8 string.
  
          :param metadata: the metadata item to set.
          :param utf8: metadata value.
  
          *New in cairo 1.16.*
  
          *New in cairocffi 0.9.*
  
          """
          cairo.cairo_pdf_surface_set_metadata(
              self._pointer, metadata, _encode_string(utf8))
          self._check_status()